1. Field of the Invention
The present invention relates to a jet air flow crusher, and particularly to a jet air flow crusher which can crush, break or grind powder grains by using jet air flows.
1. Description of the Related Art
Conventionally, jet air flow crushers have been widely used, because they are easier to maintain and operate than other types of crushers and they are very adaptable to air flow classifiers to which they are connected.
Furthermore, they have been considered to be very useful for crushing various types of powder having a low heat resistance (for example, plastic powder), because they do not produce any significant heat during their operation. These jet air flow crushers have been used not only to crush various types of powder in a narrow sense, but also to break any agglomerate of powder grains, or to remove foreign matters sticking to the surfaces of powder grains.
Various types of jet air flow crushers have been known such as those wherein nozzles are installed, for example, in a cylindrical wall to jet air from the cylindrical wall in an inward and tangential direction so as to direct the powder grains with the jet air along the inside surface of the cylindrical wall and to cause collisions between the powder grains (hereinafter referred to as "turning flow type"), wherein nozzles to jet air to carry powder grains are inwardly opposed to each other so as to enhance the collision force between powder grains (hereinafter referred to as "opposed crushing nozzle type"), wherein jet air to carry powder grains is blown against the surface of a hard wall (hereinafter referred to as "object collision type"), and wherein jet air is blown out through the partial wall of a gas phase flowing passage in the form of an ellipse and carry powder grains in the gas phase flowing passage so as to cause collisions between powder grains for crushing them (hereinafter referred to as "jet O-mizer" type).
However, these types of crushers devised or practically used have prevented several problems to solve.
For example, the "turning flow" type crushers, though applicable to the crushing processes for very small quantities of powder, present a disadvantage in that due to the construction of the mechanism to remove crushed particles from the center part of the turning air flow (generally called "classifying mechanism"), an equivalent quantity of large-sized or coarse particles is also removed with fine particles, and thus they do not possesses a sufficient industrial processing capacity. The "opposed crushing nozzle" type crushers present problems is that they are effective on only 10 .mu.m or more powder particles between which collisions take place. The "object collision" type crushers also present problems with respect to durability and contamination of foreign matter, because they cause wear of the wall against which the powder grains strike.
The "jet O-mizer" type crushers which can be provided with any apparatus for efficiently removing crushed powder particles having a uniform distribution of grain sizes. However, this type of crusher offers a problem in that it cannot sufficiently provide fine sizes of crushed powder grains thereby having a limitation in its applications.